Conventionally, writing instruments, such as water-based and oil-based marker pens and water-based ball-point pens and fountain pens, are generally provided with a cap for sealing the tip part, in order to prevent the writing instrument from becoming unable to write due to dryout of ink at the tip of the writing element.
In the case of a writing instrument having a cap as above, it is necessary to remove and attach the cap every time the pen is used and this work bothers the user if the pen is used frequently. This is why many types of so-called capless writing instruments, which do not need to have a separate cap, have been proposed.
However, such capless writing instruments, in place of a cap, need to have a sealing mechanism for sealing the front end part, in the narrow hollow interior of the writing instrument body, but such sealing mechanisms of conventional configurations are all complicated, needing many components, this results in complexity in assembly and increase in production cost.
To deal with the above problem, as a sealing method of the writing tip, Japanese Utility Model Application Laid-Open Sho 49 No. 32731 (which will be called prior art example 1, hereinbelow) discloses a configuration in which a valve plate having cuts formed radially outwardly from the center therein is arranged at the front end part inside the barrel cylinder of the writing instrument so that the writing tip can be projected through the cuts. Japanese Utility Model Application Laid-Open Sho 49 No. 107421 (which will be called prior art example 2, hereinbelow) discloses another configuration in which packings are arranged at the proximal and front ends inside the barrel cylinder of the writing instrument so that the barrel cylinder interior can be sealed and the writing tip can be projected out through the front end packing against which the tip is abutted. Still another disclosure is proposed in Japanese Utility Model Application Laid-Open Sho 63 No. 23084 (which will be called prior art example 3, hereinbelow), in which an elastic self-closing element having an opening is provided at the front part of a cap body so that the pen point of the barrel cylinder front end can projected out.
There are still other methods. Japanese Patent Application Laid-Open Hei 1 No. 281999 (which will be called prior art example 4, hereinbelow) discloses a configuration in which a sealing means is provided at the front end inside the barrel cylinder of a writing instrument so as to open and close the front end side of the sealed compartment in which the pen point of the writing element is held and the front end side of the sealed compartment is opened when the pen point is projected from the front end. Japanese Utility Model Application Laid-Open Sho 58 No. 89394 (which will be called prior art example 5, hereinbelow) discloses a method in which a sealing structure for sealing the pen tip is hermetically fitted to the front end part of the front barrel at the front end inside the barrel cylinder of the writing instrument so that it opens and closes the front part of the fixed sealing structure as the front barrel moves.
However, according to the above prior art examples 1, 2 and 3, since openings have been formed from the beginning at their sealing portions through which the pen point is projected, any of these configurations involves problems in sealing.
On the other hand, the method described in the prior art example 4 has the problem that the arrangement of the sealed compartment, seal opening and closing mechanism and the like becomes complicated. Similarly, the arrangement described in the prior art example 5 needs to provide separate parts for the sealed compartment with an opening mechanism, hence cannot avoid becoming complicated.
The present invention has been devised in view of the above conventional problems and it is therefore an object of the present invention to provide a capless writing instrument with a simple structure that can assure the sealability at the front end part inside the barrel cylinder.